<template>
	<ul class="list">
		<!-- prevent防止页面整体拖动 -->
		<li class="item" v-for="item of letters" :key="item"
			:ref="item"
			@touchstart.prevent="handleTouchStart" 
			@touchmove="handleTouchMove"
			@touchend="handleTouchEnd"
			@click="handleLetterClick"
		>{{item}}</li>
	</ul>
</template>

<script>
	export default {
		name: 'CityAlphabet',
		props:{
			cities:Object
		},
		computed:{
			letters(){
				const letters=[]
				for(let i in this.cities){
					letters.push(i)
				}
				return letters
			}
		},
		data(){
			return{
				touchStatus:false,
				startY:0,
				timer:null
			}
		},
		updated(){
			this.startY=this.$refs['A'][0].offsetTop
		},
		methods:{
			handleLetterClick(e){
				this.$emit('change',e.target.innerText)
				// console.log(e.target.innerText)
			},
			handleTouchStart(){
				this.touchStatus=true
			},
			handleTouchMove(e){
				// console.log("handleTouchMove:"+this.touchStatus)
				// console.log(e.touches[0])
				if(this.touchStatus){
					if(this.timer){
						clearTimeout(this.timer)
					}
					this.timer=setTimeout(()=>{
						const touchY=e.touches[0].clientY-79
						const index=Math.floor((touchY-this.startY)/20)
						if(index>=0 && index<this.letters.length){
							this.$emit('change',this.letters[index])
						}
					},16)
					
				}
			},
			handleTouchEnd(){
				this.touchStatus=false
			}
		}
	}
</script>

<style lang="stylus" scoped>
	@import '~@styles/varibles.styl'
	.list
		display :flex
		flex-direction :column
		justify-content :center
		position :absolute
		top:1.58rem
		right:0
		bottom :0
		width :.4rem
		.item
			line-height :.4rem
			text-align :center
			color:$bgColor
</style>
